F.4 Chem MC with explanation

2.Which of the following equations CANNOT be rewritten into an ionic equation?
(1)Zn(s)+2HCl(aq) --> ZnCl2(aq) + H2(g)
ionic eq: Zn + 2 H+→ Zn2+ + H2
(2)2Pb(NO3)2(s) --> 2PbO(s)+4NO2(g)+O2(g)
no ionic eq.
(3)Ca(OH)2(aq)+CO2(g) --> CaCO3(s) +H2O(l)
Ca2+(aq) → Ca2+(s)

Ans :B

3.Which of the following half equation are involved when iron rusts?
In rusting,
2 Fe + 2 H2O + O2 → 2 Fe(OH)2 ( Fe → Fe2+ + 2e-)
Fe(OH2) + O2 + (2x-4)H2O → Fe2O3 -xH2O (Fe2+ → Fe3+ + e-)

so Ans :C

(3)Ca(OH)2(aq)+CO2(g) --> CaCO3(s) +H2O(l)
條ionic好似係
2 OH - + CO2 -> CO3 2- + H2O

你學過redox便知道有這一道equation

第三個真的可以這樣寫成離子方程式的嗎？

2011-03-12 21:02:03 補充：
我有學過redox,但從來沒有看見過哦，書本也沒有提及
可以解釋一下嗎